ellipsoids: add functionality for ellipsoidal sets

src/ellipsoid.py

src/test/ellipsoid/__init__.py

src/test/ellipsoid/constructor.py

src/test/ellipsoid/contains.py

src/test/ellipsoid/draw_from_surface.py

src/test/ellipsoid/draw_from_volume.py

src/test/ellipsoid/norm.py